International Journal of Electrical and Computer Engineering (IJECE)

Vol. 10, No. 4, August 2020, pp. 3367~3374

ISSN: 2088-8708, DOI: 10.11591/ijece.v10i4.pp3367-3374 3367

Journal homepage: http://ijece.iaescore.com/index.php/IJECE

Voltage profile enhancement in distribution network using

static synchronous compensator STATCOM

Mohammed Y. Suliman Department of Technical Power Engineering, Technical College, Northern Technical University, Iraq

Article Info ABSTRACT

Article history:

Received Mar 9, 2019

Revised Jan 23, 2020

Accepted Feb 1, 2020

STATCOM is one of FACTS devices that used as regulator for transmission

and distribution systems which works for reactive power compensation.

STATCOM utilisation in distribution system mostly for enhancing the profile

of voltage, where used for adjusting the disturbance voltage by injecting into

the system a controllable voltage. This paper present a Fuzzy controller

based on STATCOM to enhance the voltage profile in distribution network.

The controller of STATCOM has simulated for different types of abnormal

load conditions of balance and unbalance load. The results of simulation

show ability of proposed design to enhance the load voltage which was 96%

of the nominal value.

Keywords:

D-q Theory

FACTS

Fuzzy logic

STATCOM Vsc Copyright © 2020 Institute of Advanced Engineering and Science.

All rights reserved.

Corresponding Author:

Mohammed Y. Suliman,

Department of Technical Power Engineering,

Technical College, Northern Technical University,

Mosul, Iraq.

Email: mohammed.yahya@ntu.edu.iq

1. INTRODUCTION

STATCOM is one of the most important devices can be used in power flow control and power

quality, which permit a utilise function in the prepared in the manner that without any loss the performance

expectation. The equipments such as transformer, motor, computer, printer, equipment of communication and

all types of house machines. These equipments mentioned were affect to the quality of power negatively [1].

When a large load in the network the reactive power unable to be transmitted even though with essential

of buses voltage magnitude [2]. Voltage instability cause complete or partial discontinuation in the network.

The STATCOM advantage is that can regulate efficiently the injected current in to the bus [3].

Also STATCOM has several applications in compensation of the conditions of sag/swell, the Suppressing

in harmonics of line currents and improve the power factor in the load, and reactive power compensation

in transmission line also in the load also STATCOM mitigate the fluctuations of the bus voltage [4, 5].

STATCOM with storage energy is advisable for controlling the injected voltage in its magnitude and also

the angle by VSC "Voltage Source Converter” for controlling the powers "active and reactive"

of STATCOM [6]. Many works have been suggested for the implementation of voltage profile enhancement

in the literature. Improving Voltage Profile using PI Controller in [7]. Whereas [8] presents Optimal location

of UPFC to enhence voltage profile. In [9] presents Enhancement of voltage profile using SVC. The use of PI

controller in [7], has many drawbacks that needs tunning at each operating point, slow in response and less

smoother. The use of UPFC in [8], needs settings and controllers for both STATCOM and also for SSSC.

The use of SVC in [9], have passive parameters that affect to the tuning of the system and nake some

oscillation in response. The new porposed of STATCOM for voltage profile enhancement with Fuzzy logic

control is a high-speed response and smoother than conventional controller also the propsed system use VSC

instead of passive element in SVC. The use of d-q theory to calculate the reactive power and the bus voltage

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Int J Elec & Comp Eng, Vol. 10, No. 4, August 2020 : 3367 - 3374

3368

for compensation added another feature of small-time calculation of about one cycle compared with previous

works [7],[8] and[9] that takes more than one cycle for calculation the peak amplitude, and need more

peripherals design.

2. VOLTAGE REGULATION AND COMPENSATION

The shunt device connections for regulation of bus voltage are shown in Figure 1. The model

contains power transmission line, supply (Vs), and load where the injection was in the middle of the line.

Phasor diagram, shows that line current angle has relation with the load side, which means that the active

component of current (IC) is injects to enhance the line current (Isc) and then the load voltage. The device of

current source is used for compensating the load reactive component this done by inject or absorb current (IC)

to or from the network. This lead to enhance regulation of voltage and also reduced reactive component of

the source current. Figure 2 shows Q-V characteristics of STATCOM, where the inductive load requires

enough reactive current for appropriate working so, the source should be feeding it; and this will increase

the line current from the generating area. If the feeding of reactive power is near load area, the supply current

may be reduced thus improving the voltage regulation (load side) [10]. Three methods can improve

the regulation; first by using a bank of capacitor, by using VSI "voltage source inverter" or by using CSI

"current source inverter" [11]. The STATCOM provide voltage for supporting the system under huge

abnormal condition through that the bus voltage would be deviate from the compensator normal range [12].

The main advantage of the use of voltage source converter VSC that reactive power can be generate

(instead of using capacitors) independent to the line current [13]. The three phase inverter used in inject

the controllable voltage, many techniques of modulation wrer used to implement the VSC like SPWM

(sine PWM) or SVPWM (Space Vector PWM) [14]. In distribution system the STATCOM connected before

load as shown in Figure 3[15].

Figure 1. Principles of shunt compensation Figure 2. V-Q characteristics of STATCOM

Figure 3. STATCOM connection

L1L2

X/2 X/2

VcVs Vr

Isc Icr

Vs=Vc=Vr=V

Vs

Vc

Vr

Ic

IcrIsc δ/4 δ/4

QC (C Max)

Capacitive

QL (L Max)

Inductive

Q

V

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Transient

0

FeederLine

Vs

Vi

is

L-C

Filte

r

Vdc

VLLoad

Controller

v

i

i

Int J Elec & Comp Eng ISSN: 2088-8708

Voltage profile enhancement in distribution network using static synchronous … (Mohammed Y. Suliman)

3369

3. MEASURING THE REACTIVE POWER AND LINE VOLTAGE

For measuring reactive power and line voltage, d-q theory has been applied [16]. This theory valid

for time-domain “operation in transient or steady state”, and can be applied for different current and voltage

waveforms, this allowing to design controller in real time for reactive power [17]. Also the simple of

transformation calculations, and easy to separate the alternated value and mean value respectively [18].

This theory performs by transformations known “park transformation” from a stationary to rotating

coordinates “abc to dq” [19]. The applied of dq theory (i.e. va, vb and vc) is as follows:

[

vd

vq

v0

] =2

3

[ cos(∅) cos( ∅ −

2π

3) cos(∅ +

2π

3)

−sin(∅) −sin(∅ −2π

3) −sin(∅ +

2π

3)

1

2

1

2

1

2 ]

[

va

vb

vc

] (1)

[

idiqi0

] =2

3

[ cos(∅) cos( ∅ −

2π

3) cos(∅ +

2π

3)

−sin(∅) −sin(∅ −2π

3) −sin(∅ +

2π

3)

1

2

1

2

1

2 ]

[iaibic

] (2)

∅ = (𝜔𝑡 + 𝜃) (3)

Where “ ∅ ” is phase angle between the fixed and rotating coordinates with respect to time and “θ” is angle

between voltage and current. The compensated active and reactive power:

𝑝 = 𝑉𝑑𝐼𝑑 + 𝑉𝑞𝐼𝑞 (4)

𝑞 = 𝑉𝑑𝐼𝑞 − 𝑉𝑞𝐼𝑑 (5)

The accumulated voltage is:

v = √vd2 + vq

2 (6)

4. STATCOM CONTROL DESIGN

Figure 4 shows the control system block diagram of the STATCOM. The phase voltages are

measured and the signals enter low pass filter for eliminating high frequency component. The d-q

components in (1) and (2) are calculated using “park transformation”. The aggregated voltage then calculated

using (6) this voltage is a feedback to closed loop control system, where compared with the vref set point

reference voltage of the busbar then error signals will generate verorr.

Verror = V + Vref (7)

Figure 4. Block diagram of control system

5. FUZZY LOGIC CONTROL SYSTEMS

In this study FLC “Fuzzy logic controller” was used, FLC is adequate for systems that have

mathematical model is not easy to derive [20]. Takagi-Sugeno inference mechanism systems is applied in this

study [21]. Artificial Neural Network (ANN) is used for tuning the MFs “membership functions” of

the Takagi-Sugeno [22]. The fuzzy logic control with capabilities of using the adaptive learning of ANN,

Phase Locked

Loop

vavbvc

vd

vq

2 2Park

Transformation

abc to d-q

Low Pass

Filter √Vd+Vq Σv

Vref

Fuzzy Logic

Controller

Vmax

Vmin

VSTATCOM

Verror

Ф

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3370

from this approach trained can be more easy also the rule base of Fuzzy is reduced [23]. The Fuzzy control

system constructed of 5-layers, two types of parameters in each layer some of them needs tuning other not

during step of training [24]. The details of emulating fuzzy logic control design steps for five layers output is

given in reference [25]. The two inputs universe of discourse are divide into 7 triangle MFs and

the overlap between them of 50%, the input to the controller is error and Δerror, so that for 7 MFs,

49-control rules resultant of linear functions that required to determine as shown in Figure 5a and b. To tune

these rules using ANN, 2-groups of data are used. Also 2- vectors of input: Verror and ΔVerror the output is

modulation index "m".

(a)

(b)

Figure 5. Fuzzy logic design (a) structure (b) the surface

6. SIMULATION STUDY

Study model contain feeder and changeable load of 2- load branches for balance condition and

additional load for unbalance condition as shown in Figure 6. The STATCOM in load side for compensating

the load voltage. Test the model start by load changing and continues measure the voltage at load bus

the compensation done at t=0.65 seconds for balance load as shown in Figure 7. The result shows the load

voltage drop increased proportionally as load increase, drop was maximum (0.8 pu) occur between 0.33 and

0.65 sec respectivily. Figure 8 shows the results for unbalance load action to compensate the load voltage for

unbalance condition the STATCOM mitigate and restored the load voltage drop at 0.5 seconds. Figure 9

shows the load current before and after compensation, this compensation process done by injecting voltage

VSTATCOM where phase voltage as a reference as shown in Figures 10 and 11 respectively. The FFT analysis

of the voltage of bus BB3 is shown in Figure 12, the total harmonic distorsion THD was 0.22% after injects

VSTATCOM. The power-voltage characteristic at load bus shown in Figure 13, from results can note that

the load voltage enhanced the amplitude with STATCOM and also stability margin increased.

Int J Elec & Comp Eng ISSN: 2088-8708

Voltage profile enhancement in distribution network using static synchronous … (Mohammed Y. Suliman)

3371

Figure 6. Proposed system model for simulation

Figure 7. The 3-phase waveforms of voltage at balance load

Figure 8. The 3-phase voltage at unbalance load

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time in seconds

Lo

ad

vo

lta

ge i

n P

U

STATCOM ACTION

0 0.1 0.2 0.3 0.4 0.5

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time in seconds

Lo

ad

vo

lta

ge i

n P

U

STATCOM ACTION

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Int J Elec & Comp Eng, Vol. 10, No. 4, August 2020 : 3367 - 3374

3372

Figure 9. Load current

Figure 10. The STATCOM voltage and load voltage

Figure11. The BB2 voltage with compensation

0 0.1 0.2 0.3 0.4 0.5 0.6

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time in seconds

Lo

ad

cu

rren

t in

PU

STATCOM ACTION

0 0.1 0.2 0.3 0.4 0.5-1.5

-1

-0.5

0

0.5

1

1.5

Time in seconds

Su

pp

ly V

olt

ag

e v

ersu

s L

oa

d V

olt

ag

e i

n P

U

Supply Voltage

Load Voltage

Int J Elec & Comp Eng ISSN: 2088-8708

Voltage profile enhancement in distribution network using static synchronous … (Mohammed Y. Suliman)

3373

Figure 12. The FFT analysis of the voltage of BB3

Figure 13. P-V curve

7. CONCLUSION

In this study, a STATCOM based Fuzzy logic control has been installed in load side, two cases of

disturbance conditions have been studied using MATLAB simulation the increase in load in balance and

unbalance. Results shown the compensation system with Fuzzy controller enhance the load voltage also

increase the stability margin about 20%. The simulation compared before and after inject compensation

voltage was studied for two types of load balance and unbalance condition. In two conditions the STATCOM

ability to restore the voltage of the load to the nominal value (within 97%). The use of STATCOM in

compensation more flexible and simple in design the controller and also not affect to the netwok parameters

as in [7], [8] respectively. Also fast response of design compensation system due to small computation time

compared with and [9], this important for implementation in real time.

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3374

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BIOGRAPHY OF AUTHORS

Mohammed Y. Suliman received his BSc, M.Sc. and Ph. D. degrees from University of Mosul, Iraq

in 1995, 1998 and 2014 respectively.Currently, he is a assistance professor, in the Technical College,

Northern Technical University.His research interests, include power system assessment, Power

Electronics, FACTS, Renewable energy.